In the manufacture of Italian cheese, such as Mozzarella, the milk in the cheese vat is inoculated with from approximately 2 to 4% of a bulk starter providing a mixed culture of the acid-forming organisms. In the manufacture of Mozzarella and other pasta filata cheeses, it is the practice to employ Streptococcus thermophilus together with one or more lactobacilli. Streptococci are referred to by the short name of "coccus" while the lactobacilli are referred to as "rod" bacteria because of their appearance under microscopic examination. The preferred ratio of coccus to rod cells in Italian cheese starters is from about 3:1 to 5:1. Cheesemakers have difficulty in maintaining this ratio in bulk starters, as prepared in the plant, even though culture manufacturers supply concentrates in ratios near those normally desired. Certain variations in these optimum ratios can be tolerated within the skill of the art while still producing acceptable quality cheese, but the flavor and physical properties of the cheese, such as elasticity, "stringiness," flavor, and moisture may be seriously affected unless both coccus and rod organisms are present and growing actively. To assure this, bulk starters as added to the cheese vats should at least have a coccus to rod ratio within the range from 2.5:1 to 5.5:1.
In an older practice, which has been largely abandoned by present United States cheese manufacturers, fresh whey from prior vats of Italian cheese was used as a culture medium to produce the bulk starter. Such use of liquid whey saved from previously made vats of cheese is a hazardous practice. Inhibitory compounds, heat-resistant contaminating bacteria, and equally heat-resistant bacteriophage may be present in the whey. Consequently, under present-day manufacture conditions in the United States, the culture media for preparing Italian cheese bulk starters comprises reconstituted non-fat dry milk (NFDM) singly or in combination with various levels of sweet-whey. Reconstituted NFDM is an expensive cultue medium because of the high price of non-fat dry milk. It is the medium of choice, however, because it is a dependable material which can be pretested. It would be very desirable to find a much less expensive culture medium for producing Italian cheese bulk starters with the proper coccus to rod ratios, which medium would be as dependable, safe, and subject to pretesting as NFDM-based media.
Attempts have been made to develop whey-based media for preparation of bulk starters, for the manufacture of cheese, including Italian cheeses. Both fresh whey and reconstituted dried sweet-whey have been used. U.S. Pat. No. 2,805,950 describes the preparation of bacterial cultures for use in the making of Swiss cheese. Streptococcus thermophilus either alone or in combination with lactobacilli are cultured in whey, such as fresh whey from a prior Swiss cheese making operation, and after completion of the culturing, from 5 to 15% of milk powder is added, and the incubated culture is frozen to be held for future use. As recognized in this patent (col. 3, line 61, et seq.), a major problem in making Swiss cheese has been in obtaining the proper coccus to rod proportions. The patent recommends preparation of pure cultures of coccus (S. thermophilus) and separate pure cultures of rods (lactobacilli), which are then mixed in the proper proportions for use in the cheese vats. Preferably, therefore, the process of the patent involves the cultivation in a whey culture of Streptococcus thermophilus substantially free from lactobacilli.
U.S. Pat. No. 3,852,158 describes a bulk starter medium, which can be prepared in dry form, from milk products or derivatives including sweet-whey, NFDM, acid-whey powder, buttermilk powder, whole-milk powder, and mixtures thereof. One preferred formulation contains a major amount of sweet-whey and a minor amount of NFDM. The culture media is characterized by containing citrate. It is recommended for use in preparing a wide variety of cheese starter cultures.
Cottage, Swiss, and Italian bulk culture manufacture with a whey-based bacteriophage inhibitory medium under pH control is described by W.L. Chen and G.H. Richardson, J. Dairy Sc., Vol. 58, No. 5, pp. 785-786. Both acid-whey and sweet-whey were tested but not in combination.
During the experimental work leading to the present invention, it was found that neither reconsituted dried sweet-whey or reconstituted dried acid-whey were satisfactory media for producing Italian cheese bulk starters. Acid-whey inhibits the growth of both the coccus and rod bacteria. With sweet-whey, the lactobacilli are inhibited with the result that the ratio of coccus to rod is much greater than desired. Partially delactosed sweet-whey results in even greater disparities in the desired coccus to rod ratios, the coccus growing profusely while the rods grow poorly. None of these whey media are, therefore, comparable to reconstituted NFDM for the production of Italian cheese bulk starters.